Preparation Of Cellulose Nanocrystals Research Articles

Efficient preparation of cellulose nanocrystals and regulation of cholesteric liquid crystals for advanced anti‐counterfeiting

AbstractCellulose nanocrystals (CNCs) can self‐assemble to form cholesteric liquid crystal, which make it one of the most promising optical materials at present. CNCs can be produced by sulfuric acid hydrolysis. It is found that hydrolysis conditions influence the existing form of reaction components and their reaction activities, which leads to different reaction routes and mechanisms under varied reaction conditions, with CNCs of varied quality produced. High‐quality CNC with more uniform particle size could be prepared at a critical acid concentration of 64 wt%, which was used to study the formation process of CNC liquid crystal and the structure regulation of cholesteric liquid crystal. By adjusting the drying temperature and adding a small molecule of water‐soluble chitosan (WSC) can well regulate cholesteric liquid crystal and change the pitch of a film, and the reflection wavelength can be redshifted, thus enriching texture patterns and creating distinctive color. Suitable addition of WSC can enhance the multi‐domain effect during liquid crystal formation process and finally creates more colorful film with fine texture. The rich and tunable liquid crystal characteristics endowed by WSC addition is irreplicable and artistic, which helps to realize the great potential application of the composite film in advanced anti‐counterfeiting.

Green preparation of cellulose nanocrystals and nanofibers by ball milling assisted citric acid hydrolysis

In order to solve the drawbacks of carboxylated cellulose nanocrystals (CNCs) prepared by critic acid (CA) hydrolysis method, such as low yield and low esterification degree, herein, ball milling assisted citric acid hydrolysis method was applied to obtain carboxylated CNCs and cellulose nanofibers (CNFs) with fine and uniform size, high yield and carboxyl content, good crystallinity, and good thermal stability. It was discovered that the diameter of CNCs and CNFs were decreased and the size uniformity was improved. The yield of CNCs was obviously improved to 39.8% due to the promoted esterification reaction, which was 3.3 times of that without ball milling. Moreover, the carboxyl group content of CNCs and CNFs were improved to a maximum of 0.52 and 0.48mmol/g, respectively. As ball milling progressing, more amorphous regions were destroyed and cellulose bundles were dissociated, resulting in CNCs and CNFs with high crystallinity. The thermal decomposition temperature of CNCs and CNFs were ranged from 317 to 331℃, which was higher than that had reported. This work provided an effective route for carboxylated CNCs with good yield, esterification degree and other performance, which was beneficial for the subsequent applications in the field of biomaterials.

Transparent, thermal stable, water resistant and high gas barrier films from cellulose nanocrystals prepared by reactive deep eutectic solvents.

Nanocellulose-based film, as a novel new type of film mainly made of nanosized cellulose, has demonstrated an ideal combination of renewability and enhanced or novel properties. Considerable efforts have been made to enhance its intrinsic properties or create new functions to expand its applications, such as in food packaging, water treatment or flexible electronics. In this paper, two different types of deep eutectic solvents (guanidine sulfamate-glycerol and guanidine sulfamate-choline chloride) were formulated and applied to prepare cellulose nanocrystals with dialdehyde cellulose (DAC). The effects of reaction conditions including time, temperature and cellulose-DES ratio on the grafting degree and yield were studied. After ultrasonication, two types of CNCs, with an average diameter of 3-5nm and an average length of 140.7-204.2nm, were obtained. The synthesized CNCs displayed an enhanced thermal stability compared to pristine cellulose. Moreover, highly transparent (light transmittance higher than 90%) and water stable nanocellulose based films (a wet tensile strength of higher than 30MPa after immersing in water for 24h) were fabricated. Besides, the obtained films exhibited low oxygen transmission rate, showing a good potential application in food packaging.

Screening of Miscanthus Genotypes for Sustainable Production of Microcrystalline Cellulose and Cellulose Nanocrystals

Miscanthus spp. has been regarded as a promising industrial plant for the sustainable production of bio-based materials. To assess its potential for microcrystalline cellulose (MCC) and cellulose nanocrystals (CNCs) production, 50 representative clones of M. sinensis and M. floridulus were selected from a nationwide collection showcasing the extensive diversity of germplasm resources. Descriptive analysis indicates that the dry biomass weight of M. floridulus is advantageous whereas M. sinensis demonstrates higher MCC and CNCs yields as well as a smaller CNCs particle size. Correlation analyses indicated that MCC yield is solely influenced by the cellulose content whereas the yield of CNCs is affected by both the cellulose content and CrI. Comparative analyses of the chemical composition, physical features (degree of polymerization, crystalline index, particle size distribution and zeta potential), and scanning electron microscopy indicated that the MCC and CNCs extracted from M. sinensis and M. floridulus exhibited remarkable stability and quality. Additionally, the CNCs derived from M. sinensis and M. floridulus exhibited a distinctive ball-shaped structure. Notably, machine learning has demonstrated its efficacy and effectiveness in the high-throughput screening of large populations of Miscanthus spp. for predicting the yield of MCC and CNCs. Our results have also laid the theoretical foundation for the exploration, cultivation, and genetic breeding of M. sinensis and M. floridulus germplasm resources with the purpose of MCC and CNCs preparation.

A Machine Learning Aided Yield Prediction Model for the Preparation of Cellulose Nanocrystals

A Machine Learning Aided Yield Prediction Model for the Preparation of Cellulose Nanocrystals

Life cycle assessment of cellulose nanocrystals prepared from crop straw by sequential periodate-chlorite oxidation

Life cycle assessment (LCA) of cellulose nanocrystals (CNC) prepared by sequential periodate-chlorite oxidation (SPCO) remains limited. In this study, the environmental impacts of CNC preparation at lab (LAB) and industrial (IND) scales were assessed based on the eFootprint system and data from the Chinese Life Cycle Database (CLCD). At the LAB scale, the global warming potential (GWP) reached 3410 kg CO2 eq/kg CNC. The contributions of the U2 (pulp making), U3 (periodate oxidation), U5 (concentration), and U6 (freeze-drying) unit processes were 42.9%, 22.8%, 21.3%, and 10.6%, respectively. At the IND scale, the GWP was reduced by one order of magnitude to 141 kg CO2 eq/kg CNC, and most of the other 13 category indicators of environmental impact (acidification, eutrophication, ecotoxicity, human toxicity, etc.) also showed the same trend. The contribution of the unit process U5 exceeded 50% in the 12 environmental impact indicators. The large contribution of U5 was attributable to the extensive use of ethanol. At the industrial scale, the GWP was reduced to 22.7 kg CO2 eq/kg CNC when the periodate was recycled, and an ultrafiltration membrane system was used to concentrate CNC solutions. The environmental impact of CNC prepared by SPCO was lower than that of CNC prepared by sulfuric acid hydrolysis. This study comprehensively assessed the potential environmental impacts of CNC production on an industrial scale and provided valuable data for future industrial-scale production of CNC and for comparison with alternative products.

Extraction and preparation of cellulose nanocrystal from Brewer's spent grain and application in pickering emulsions

In recent years, the search for novel Pickering stabilizers has attracted much interest in the food, cosmetic and pharmaceutical industries. In this work, brewer's spent grain cellulose (BSGC) was successfully extracted by diluted acid, alkaline and bleaching treatments, and then brewer's spent grain cellulose nanocrystal (BSGCNC) were obtained by acid hydrolysis treatment of BSGC. The properties of the BSGCNC were characterized, and the results showed that the BSGCNC had a rod-like structure with high crystallinity (67.09%). Then the emulsification properties of BSGCNC were evaluated by different concentrations and water-oil ratios, and the results showed that BSGCNC were able to form stable Pickering emulsions. This study suggested that cellulose nanocrystal (CNC) could be extracted from brewer's spent grain which was used as food waste, as a stabilizer for Pickering emulsions.

Electromediated Oxidation of Hydrolysed Bacterial Cellulose

The state-of-the-art method to isolate cellulose nanofibres employs a 2,2,6,6-Tetramethylpiperidinyloxyl (TEMPO)/NaBr/NaClO system, where the primary alcohols on the surface of cellulose microfibrils are oxidised. However, the large consumption of hypochlorite in this system makes it problematic for industrial implementation. Previously, electrochemical oxidation with a TEMPO catalyst has been reported for the preparation of cellulose nanofibres. Here, we present a study on the electromediated oxidation of bacterial cellulose (BC), the purest form of cellulose. BC has been used in a hydrolysed form, enabling the electromediated preparation of cellulose nanocrystals (CNCs), which is generally deemed even more costly than the preparation of cellulose nanofibres.In this work, the electromediated oxidation and cyclic voltammetry were performed in an electrochemical cell, which featured three electrodes: A Hg|Hg2SO4|K2SO4 reference electrode, a titanium net counter electrode, and a carbon foam working electrode, offering a high surface area. A static potential of 0.5 V was applied during the chronoamperometry and explored oxidation times were 3, 5, 9, 12 and 24 h.Using a TEMPO catalyst, the electromediated oxidation was applied to hydrolysed and non-hydrolysed BC fibres in a pH 10 buffer. The C6 primary hydroxyls of BC were successfully converted to sodium carboxylate groups. By the application of the TEMPO electro-mediated oxidation to hydrolysed BC for 9 h, high carboxylate and aldehyde concentrations of 1.4 and 0.3 mmol/g, respectively, were formed in the oxidized fibre. The carboxylate and aldehyde content was determined by a conductometric titration method. Surface morphologies after oxidation were investigated, showing alteration of the microfibril morphology for BC and the production of cellulose nanocrystals for hydrolysed BC. Hence, we present an effective and environmentally friendly route, which is particularly suitable for the preparation of cellulose nanocrystals.

Cellulose rubber foam composite use as oil absorbent

The focus of this study was to explore the fabrication of cellulose rubber foam (CRF) using kapok fibers (KF) as an oil absorbent material. Chemical methods such as sodium hydroxide surface treatment, hydrogen peroxide treatment, and acid hydrolysis were employed to prepare cellulose nanocrystals (CNC). The results of the nuclear magnetic resonance (NMR) spectroscopy test indicated that the chemical modification of kapok fiber resulted in the removal of lignin and hemicellulose by a disappearing peak at 17, 52, and 148 ppm, respectively. Hydrolysis process of the kapok fiber resulted in nanometer-sized cellulose, with a yield of 72% as revealed by transmission electron microscopy (TEM). The amount of cellulose nanocrystals from kapok fiber (KF-CNC) used in the study varied from 0 to 5 phr during the formation of the cellulose rubber foam, and it was found that the foam density increased as the number of cellulose nanocrystals from kapok fiber increased. Additionally, the percentage of collapse from the compressive strength of cellulose rubber foam decreased as the amount of cellulose nanocrystals from kapok fiber increased. Fourier transform infrared spectroscopy (FTIR) confirmed the incorporation of cellulose nanocrystals from kapok fiber into the rubber foam (RF) as the amount of cellulose nanocrystals from kapok fiber increased. The oil absorbent of cellulose rubber foam composite with 1 phr cellulose nanocrystals from kapok fiber show highest absorption capacity was 17.8 g/g. The cellulose rubber foam composite absorbs oil before absorbing water when water and oil are combined. Moreover, the cellulose rubber foam could be reused more than 50 times.

Impact of ionic liquid's cation alkyl chain length and reaction time on cellulose nanocrystals preparation

Traditional methods to obtain cellulose nanocrystals typically involve mechanical and chemical processes and develop an improved process in terms of efficiency, sustainability, and the quality of CNCs produced are interesting. In this sense, we aimed to prepare cellulose nanocrystals (CNCs) from the hydrolysis of microcrystalline cellulose using protic ionic liquids (PILs), named 3-diethylamino-propylammonium hexanoate ([DEAPA][Hex]), 3-dimethylamino- 1-propylammonium hexanoate ([DMAPA][Hex]), and propylammonium hexanoate ([PA][Hex]) at different reaction times. The PILs demonstrated efficiency in producing cellulose nanocrystals, regardless of the cation size and reaction times. However, as expected the properties of the CNCs varied depending on the studied condition. The highest yield was observed in DMAPA[Hex], with a 34 % conversion. Crystalline indices decreased independent of the cation sizes and reaction times. Thermal stabilities were shifted to higher temperatures up to 92 ºC probably due to PILs cation sizes. In contrast, increasing reaction times decreased nanocrystals’ thermal stabilities up to 51ºC. So, protic ionic liquids (PILs) can be considered more environmentally friendly or sustainable solvents compared to traditional organic solvents for preparing cellulose nanocrystals. In the present work, it is reported an alternative method for obtaining CNCs and additionally provide the best preparation conditions for achieving important properties of this nanomaterial, with the potential for various applications.

Preparation and characterization of cellulose nanocrystals with high stability from okara by green solvent pretreatment assisted TEMPO oxidation

Because the traditional preparation methods of cellulose nanocrystals (CNCs) involve chemical pollution issues, in this study, two typical green solvents, alkali/urea solvent (AUS) and deep-eutectic solvent (DES), were used to dissolve insoluble soybean fibers (ISF) extracted from okara and prepare regenerated CNCs (AUS/CNC and DES/CNC), which were further modified by TEMPO oxidation (AUS/T-CNC and DES/T-CNC). The recoveries of AUS and DES were 82.58 % and 84.00 %, respectively. Chemical composition analysis showed high cellulose purity (>95 %) of the regenerated CNCs. FTIR, XRD and 13C NMR analysis indicated the cellulose structure and polymorph of CNCs. Thermal analysis revealed that the maximum degradation peak of regenerated CNC shifted to a lower temperature. AFM revealed that CNCs exhibited rod-like fiber structures, while AUS-pretreated CNCs exhibited some special spherical fibers. TEMPO oxidation showed an enhancement effect on the characteristics of AUS/T-CNC and DES/T-CNC; DES/T-CNC exhibited higher stability and apparent viscosity than AUS/T-CNC. The DES/T-CNC-based cryogel displayed a higher adsorption capacity for anthocyanin (0.40 g/g) and curcumin (1.09 g/g) with good controlled release capacity. These results indicated that green solvent pretreatment-assisted TEMPO oxidation is a new environmentally friendly and low-cost method for the preparation of CNCs and shows excellent potential in the field of drug loading and controlled release.

Carboxylation of sulfated cellulose nanocrystals by family AA9 lytic polysaccharide monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) from the auxiliary activity 9 (AA9) family act on cellulose through an oxidative mechanism that improves cellulose saccharification in concert with other cellulolytic enzymes. Degradation and solubilization of cellulose chains are known to take place when various cellulose hierarchies, fibers, nanofibers, and cellulose nanocrystals (CNCs) are subjected to LPMOs, either alone or in combination with other cellulose acting enzymes. The use of LPMOs to modify and prepare CNCs has been proposed mostly in top-down synthesis from larger hierarchies. Here, we attempted a direct surface modification of CNCs with LPMOs with the aim of investigating the role played by the charged sulfate groups on CNCs. Sulfate half-ester groups are introduced during the preparation of CNCs from cellulose using sulfuric acid. It has been proposed that the charged sulfate groups hinder the binding of enzymes or affinity of charged reactants on the surface and hence reduce enzymatic and chemical reaction efficiency. We demonstrate the modification of commercial sulfated CNCs using a family AA9 LPMO. Conductometric titration and spectrometric characterization of the oxidized particles indicate that carboxylation of up to 10% was possible without degradation of the crystals. Unexpectedly, the carboxyl groups could only be introduced to the crystals containing sulfate groups, while desulfated crystals remained unfunctionalized. This was deemed to be due to that the sulfate groups limit the adsorption of the enzymes and hence modulate the cuts facilitated by the enzymes on the surface. This limits the release of chains from the surface and enables the carboxylation of the insoluble substrate rather than the release of the solubilized chains. This study highlights the importance of analyzing both the solid and soluble reaction products to gain insights into the oxidation mechanism. We demonstrated that 10% functionalization suffices for the use of CNCs in coupling chemistry.

Preparation of cellulose nanocrystals from commercial dissolving pulp using an engineered cellulase system

There is increasing attention to the production of cellulose nanocrystals (CNCs) from lignocellulosic biomass by enzymatic hydrolysis with cellulase. In this study, the feasibility of the application of a cellulase system from engineered strain Penicillium oxalicum cEES in the production of CNCs was assessed. Using commercial eucalyptus dissolving pulp (EDP) as substrate, the CNCs were successfully obtained by enzymatic hydrolysis with the cellulase cEES, and the total yields of CNCs reached 15.7% through three-step enzymatic hydrolysis of total 72 h (24 h for each step). The prepared CNCs were characterized and found that their crystallinity and thermal stability were higher than that of EDP. In the later stage of enzymatic hydrolysis, the process efficiency of enzymatic preparation of CNCs greatly decreased because of the high crystallinity of cellulosic substrate, and a simple homogenization treatment can promote the enzymatic hydrolysis, as well as produce fusiform CNCs with more uniform size and more fermentable sugar that could be further converted into fuels and bulk chemicals through fermentation. This study provides a feasible enzymatic preparation process for CNCs with engineered cellulase and commercial cellulosic materials.Graphical

Production and Characterization of Cellulose Nanocrystals from Eucalyptus Dissolving Pulp Using Endoglucanases from Myceliophthora thermophila

Endoglucanase (EG) is a key enzyme during enzymatic preparation of cellulose nanocrystals (CNCs). Myceliophthora thermophila is a thermophilic fungus that has thermal properties and a high secretion of endoglucanases (EGs), and could serve as potential sources of EGs for the preparation of CNCs. In this work, four different GH families (GH5, GH7, GH12, and GH45) of EGs from M. thermophila were expressed and purified, and their enzymatic characteristics and feasibility of application in CNC preparation were investigated. It was shown that the MtEG5A from M. thermophila has good potential in the enzymatic preparation of CNCs using eucalyptus dissolving pulp as feedstock. It was also observed that there was a synergistic effect between the MtEG5A and other MtEGs in the preparation of CNCs, which improved the yield and properties of CNCs obtained by enzymatic hydrolysis. This study provides a reference for understanding the enzymatic characteristics of different families of EGs from M. thermophile and their potential application in nanocellulose production.

Freeze-thaw assisted maleic acid pretreatment of eucalyptus to prepare cellulose nanocrystals and degraded lignin

A green and effective method is proposed for the pretreatment of eucalyptus by freeze–thaw assisted maleic acid tactic, wherein the effects of freeze–thaw, maleic acid concentration, reaction time, and temperature on the fractionation were examined. Results showed that under optimal conditions (60% maleic acid, 120 °C, and 2 h), a remarkable removal of 74.5% lignin and 95.2% hemicellulose was achieved after freeze–thaw treatment. The resulting cellulose-rich solid residues were further processed with maleic acid to prepare cellulose nanocrystals, which displayed uniform sized rod-like structures and high crystallinity (62.51%). Moreover, maleic acid pretreatment resulted in lignin with low molecular weight (2110–2530) and excellent homogeneity (PDI ≤ 1.86), while maintaining a relatively intact structure. The lignin had high β-O-4 aryl ether bond contents (≥77.5%) and abundant phenolic hydroxyl contents (2.33–3.63 mmol/g). Overall, the process exhibits notable benefits in effectively separating lignocellulose for high valorization.

Prediction and analysis of preparation of cellulose nanocrystals with machine learning

Prediction and analysis of preparation of cellulose nanocrystals with machine learning

Life cycle assessment and mechanical properties of nanocomposites based on cellulose nanocrystals

AbstractThe present work focuses on the preparation of cellulose nanocrystals (CNCs) reinforced composites based on polyhydroxybutyrate (PHB) and polypropylene (PP). The effects of the CNCs content as reinforcement and the addition of maleic anhydride (MA) as a coupling agent on the mechanical and morphological properties of the composites were studied. In addition, the biodegradability of the composites was investigated. Samples were prepared using PP and PHB as matrixes and CNCs as reinforcement. Test samples were prepared using the injection molding machine. The studied parameters were microscopic analysis and tensile strength measurement. Tensile strength increased with increasing CNC, but it decreased slightly when 5 wt% of CNC was added. Tensile strength decreased with the addition of MA. Environmental impacts from the production of 100 g of PP and PHB were evaluated using the life cycle assessment (LCA) approach. The results showed that the environmental impacts of composites containing PHB biopolymer are higher than PP ones.

Preparation of Cellulose Nanocrystals by Synergistic Action of Ionic Liquid and Recyclable Solid Acid under Mild Conditions

Cellulose nanocrystals (CNCs) are nanoscale particles made from cellulose. They have many unique properties such as being lightweight, stiff, and renewable, making them promising for a variety of applications in a wide range of industries, including materials science, energy storage, and biomedicine. In this paper, a two-stage (swelling-SA-catalyzed) method including IL pretreatment and solid acid hydrolysis process was developed to extract CNCs with high purity and good thermal stability from microcrystalline cellulose (MCC). In the first stage, the swelling of MCC in ionic liquid was studied with the assistance of ultrasonication, and it was found that the amorphous regions became more disordered while the crystalline areas were selectively retained under the conditions of 30 min of reaction time, 45 °C of temperature, 2% of ionic liquid water content and 1:4 mass ratio of cellulose to ionic liquid. CNCs were extracted using solid acid hydrolysis, with a 45 wt% solid acid to cellulose ratio and a 5.0 h hydrolysis process at 45 °C. The morphology, crystallinity, surface characteristics and thermo stability of the sample were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Results demonstrated the highly thermostable CNCs were successful extracted with rodlike shape of 300 ± 100 nm in length and 20 ± 10 nm in width. Solid acid recovery and reuse were also studied, revealing a promising candidate that can reduce the environmental impact associated with chemical products.

Investigation of the Effect of Process Parameters on Fabrication of Nanocrystalline Cellulose from Crotalaria Juncea

ABSTRACT Crotalaria juncea bast fibers a novel cellulose rich material is valorized by producing cellulose nanocrystals (CNCs) which gained much attention due to its unique properties. CNCs obtained during this study consisted of two steps: pretreatment of C. juncea fibers to obtain chemically purified cellulose followed by sulfuric acid hydrolysis. Efficacy of two different pretreatment methods chlor-alkali method (pre-treatment-I) and ultra sound assisted chlorine free alkaline peroxide (pre-treatment-II) methods was examined for CNC preparation. Pre-treatment-I was found to be more effective yielding higher crystallinity and higher surface sulfate ester groups containing CNCs compared to CNCs obtained using pre-treatment-II. Moreover the cellulose structure was altered with more pure cellulose-I structure obtained from pre-treatment-I. The process conditions of pre-treatment – I was optimized for CNC preparation. The acid concentration of 80%(w/v) was found to be optimized to produce CNCs with~43% yield, 80.9% crystallinity index having a rod-like structure (Length −120 ± 26 nm and diameter − 25 ± 5.5 nm). The surface charge density of the optimized CNC was found to be 0.34 meqv/g and a zeta potential −27.7 mV was recorded emphasizing stable dispersion.

Preparation of Cellulose Nanocrystals: Controlling the Crystalline Type by One-Pot Acid Hydrolysis.

Cellulose nanocrystals (CNCs) have aroused increasing interest owing to their renewable origin and excellent properties derived from their size and morphology. Based on their chain orientation, CNCs can be prepared as two main allomorphs (I or II). However, achieving pure CNC allomorphs still requires enhanced control on the CNCs synthesis process and improved understanding of the involved reaction parameters. In this work, we study in detail a set of parameters for CNC synthesis using one-pot acid hydrolysis and evaluate their influence on the outcome with respect to yield, purity, and repeatability. We also demonstrate that a fast, nondestructive, and accurate methodology based on dynamic light scattering is an efficient alternative to the usual structural analysis of the synthesis outcome. Finally, we provide an improved protocol to reliably obtain each allomorph with mass yields of 25% for type I and 40% for type II. Emphasis is put on the reduction of the environmental impact and the overall preparation time.